The effect of m-AMSA, an effective chemotherapeutic agent used in the treatment of leukemia, on spontaneous monocyte-mediated cytotoxicity (SMMC) was investigated. Using the cytotoxicity assay previously described, it was found that pulsing peripheral MNLs with m-AMSA for 15 minutes had no effect on SMMC. However, when doses of 0.1-1 M were left in vitro throughout the culture period, AMSA increased SMMC 2-4 fold. Using a 72 hour continuous infusion protocol to give m-AMSA IV to patients with varius malignancies, we are presently studying the effect of this agent in vivo on SMMC.